Lubricated Diamond Bearing Drill Bit

Abstract

A method for lubricating a diamond bearing system of a downhole well tool involves dispensing a polyol lubricant for the reduction of friction between the two diamond surfaces. The lubricant forms a reduced friction surface film on the diamond. The polyol lubricant may be mixed with water. The polyol lubricant may contain ethylene glycol, glycerol, or a combination with water.

1 . A method for lubricating a diamond bearing system of a downhole well tool comprising:
 dispensing a polyol lubricant for the reduction of friction between two diamond surfaces in a sealed diamond bearing system of a well tool.   
   
   
       2 . The method of  claim 1 , wherein the well tool comprises an earth boring bit. 
   
   
       3 . The method of  claim 1 , wherein the polyol lubricant is mixed with water. 
   
   
       4 . The method of  claim 1 , wherein the polyol lubricant consists substantially of ethylene glycol, glycerol, or a combination thereof. 
   
   
       5 . A down-hole drilling tool comprising:
 a head section;   a bearing shaft extending from the head section;   an external region of the bearing shaft having a diamond contact surface;   a cutter rotatably mounting on the bearing shaft;   an internal region of the cutter having a diamond contact surface, the internal region of the cutter being in a sliding relationship with the external region of the bearing shaft; and   a sealed lubrication system for the reduction of friction between the external region of the bearing shaft and the internal region of the cutter, the sealed lubrication system comprising:
 a lubricant comprising an organic compound having a minimum of two hydroxyl groups; 
 a seal assembly for retaining the lubricant in the lubrication system; and 
 a pressure compensator for reducing the pressure differential between the polyol lubricant and drilling fluid on the exterior of the drilling tool. 
   
   
   
       6 . The drilling tool of  claim 5 , wherein the lubricant is mixed with water. 
   
   
       7 . The drilling tool of  claim 5 , wherein the lubricant consists substantially of ethylene glycol, glycerol, or a combination thereof. 
   
   
       8 . A downhole well tool comprising:
 a sealed bearing system;   a rotating bearing surface having a diamond contact surface, a stationary bearing surface having diamond contact surfaces in sliding engagement with the rotating bearing surface; and   a polyol lubricant for the reduction of friction, wherein the polyol lubricant consists substantially of ethylene glycol, glycerol, or a combination thereof.   
   
   
       9 . The drilling tool of  claim 8 , wherein the polyol lubricant is mixed with water.